This invention pertains to a user interface device which is designed to control multiple parameters of several electronic filter types commonly used in audio spectrum processors. The filter types which can be controlled by the invention include bell filters, notch filters, shelving filters, and pass-band filters. These filter types are employed in commercial products such as parametric equalizers, graphic equalizers, paragraphic equalizers, notch equalizers, shelving equalizers, and frequency-dividing crossover units.
Bell Filter. A bell filter is a filter type which amplifies or attenuates the signal amplitude over a limited frequency band or region. In general, a bell filter has three parameters which can be controlled. The first parameter which can be controlled is the center frequency of the filter. The second parameter which can be controlled is the bandwidth of the filter. Alternatively, the filter quality factor, or "Q" can be controlled which is the same as controlling the bandwidth in an inverse relationship, where Q and bandwidth are related by: EQU Q=center frequency/bandwidth (1)
The third parameter which can be controlled is the amplitude at the center of the filter region. An amplitude control is also commonly called a "gain", "level", or "boost/cut" control, where a "boost" setting corresponds to an increased amplitude over the filter region and a "cut" setting corresponds to a decreased amplitude over the filter region. Bell filters are commonly employed in commercial products such as graphic equalizers, para-graphic equalizers, and parametric equalizers, where one, two, or all three of the parameters described may be controlled.
Notch Filter. A notch filter is a filter type which attenuates the signal over a limited frequency band or region and attenuates the signal to zero amplitude at the center of the attenuation region of the filter. In general, a notch filter has two parameters which can be controlled. The first parameter which can be controlled is the center frequency of the filter. The second parameter which can be controlled is the bandwidth of the filter. Alternatively, the filter Q can be controlled which is the same as controlling the bandwidth in an inverse relationship, where Q and bandwidth are related by equation (1). Notch filters are commonly employed in commercial equalizer products, where one or two of the parameters described may be controlled.
Shelf Filter. A shelf filter is a filter type which amplifies or attenuates the signal amplitude by a constant factor over a defined frequency region. In general, a shelf filter has three parameters which can be controlled. The first parameter which can be controlled is the transition frequency of the filter from one constant amplitude region, or "plateau" to an adjacent plateau region. The transition frequency may be defined as the frequency at which the amplitude is 3 dB different from the amplitude in one or the other plateau region, or the transition frequency may be defined as the frequency half-way between the two plateau regions of which the latter definition will be used throughout this patent disclosure. The second parameter which can be controlled is the amplitude level over the shelf plateau region. The third parameter which can be controlled is the shelf slope over the transition region from one plateau to the adjacent plateau. Shelving filters are commonly employed in commercial products such as equalizers and frequency-dividing crossovers, where one, two, or all three of the parameters described may be controlled.
Pass-band Filter. A pass-band filter is a filter type that passes the signal over a given frequency band or region and attenuates (or "rejects" or "stops") the signal over an adjacent frequency band(s) or region(s). The three parameters of a pass-band filter which are of interest in this patent disclosure are the pass-band corner frequency (also called the "cut-off" or "-3 dB" frequency), pass-band amplitude, and filter slope over the transition from the pass-band region to the stop-band region. A pass-band filter differs from a shelf filter in that a pass-band filter is intended to attenuate completely, or "stop" the audio signal over some region. The first parameter which can be controlled is the pass-band corner frequency. The second parameter which can be controlled is the amplitude of the filter over the pass-band region. The third parameter which can be controlled is the slope of the filter over the transition region between the band-pass-band region and the band-stop region. Pass-band filters are commonly employed in commercial products such as frequency-dividing crossovers, where one, two, or all three of the parameters described may be controlled.
Some of the objectives of a good user interface apparatus for the control of an audio spectrum processor include: 1) a placement of control elements and motion of operation which provides an intuitive relationship to the resulting frequency response of the filters, 2) an economical design which minimizes the number of control elements and the area necessary to arrange the controls, 3) a minimum set of control elements that still allows control of all the parameters for a given filter, 4) a single common user interface apparatus with a minimum set of control elements that allow the intuitive control of more than one type of filter, 5) a set of control elements that allow more than one rate of continuous filter change to be made, 6) a minimum set of control elements that allow the control of two or more filter parameters simultaneously, and 7) an ergonomic design which allows the control of multiple filter parameters and multiple filter types comfortably using one hand with the wrist confined to one location. Prior art devices have continued to be less than satisfactory, or completely void of accomplishing some of these objectives. Most user interface control devices used in commercial audio spectrum processors are deficient in one or more of the above mentioned objectives.
A common user interface control apparatus used in commercial parametric equalizers for the control of a bell filter is shown in FIG. 1, where each of the three parameters of center frequency, bandwidth, and amplitude are controlled by individual rotary controls. One deficiency of this type of user interface is that the placement of the controls and the motion of operating the controls does not provide an intuitive relationship to the resulting filter frequency response. Another deficiency of this type of interface is the necessity of two hands to operate two controls simultaneously.
Another common user interface control apparatus used in commercial parametric equalizers for the control of a bell filter is shown in FIG. 2, where one of the three parameters of center frequency, bandwidth, and amplitude are selected by a pushbutton key and then a common rotary thumb-wheel control is used to adjust the selected parameter. One deficiency of this type of user interface is that the placement of the controls and the motion of operating the controls does not provide an intuitive relationship to the filter frequency response. Another deficiency of this type of interface is that only one parameter can be adjusted at any given time.
Common user interface control devices for notch filters also include those of FIG. 1 and FIG. 2 except the amplitude controls are not present. The deficiencies already described for the control of bell filters also applies to the control of notch filters using the user interface control devices shown in FIG. 1 and FIG. 2.
A common user interface control apparatus used in commercial frequency-dividing crossover processors consisting pass-band filters also include those of FIG. 1 and FIG. 2, where the center rotary control in FIG. 1 operates the filter slope adjustment or the center pushbutton in FIG. 2 selects the slope parameter. The deficiencies already described for the control of bell filters also applies to the control of pass-band filters using the user interface control devices shown in FIG. 1 and FIG. 2.
A common user interface control apparatus used in commercial graphic equalizers comprising of a plurality of evenly-spaced, fixed-frequency bell filters is shown in FIG. 3. This interface provides a good intuitive relationship of the placement of the "slider" controls with the resulting response of the filter settings. One deficiency of this type of user interface is the potentially large number of control elements needed to implement a graphic equalizer which has a large number of ball filters. Another deficiency of this type of user interface is the potentially large area needed to accommodate the large number of controls. Furthermore, this arrangement of control elements would not be suited for the control of bell filters which have a variable center frequency, or for the control of pass-band filter types
Another common user interface control apparatus used in commercial graphic equalizers comprising of a plurality of bell filters is shown in FIG. 4, where a particular bell filter is selected by depressing one of the pushbutton keys, then the amplitude is adjusted using the common rotary thumb-wheel control. This interface is less intuitive than that of FIG. 3 and requires one more control element which makes this user interface less satisfactory than that of FIG. 3.
The user interface control apparatus shown in FIG. 5 provides a similarly intuitive operation as that shown in FIG. 3 by providing a pair of "boost/cut" pushbutton keys for each bell filter but suffers from the same deficiencies and requires twice as many control elements compared to that shown in FIG. 3.
Another common user interface control apparatus used in commercial graphic equalizers is that as shown in FIG. 6, where the left and right pushbutton keys select a particular bell filter and the top and bottom pushbutton keys increase and decrease the selected filter's amplitude respectively. While this user interface is intuitive to operate and requires only a minimal number of control elements, it is deficient in that the four keys alone can only operate at one rate of continuous change in either filter selection or filter amplitude. Furthermore, this user interface comprising of the four keys alone could not control more than two parameters of a given filter type.
The present invention is premised on accommodating all of the objectives described above to a satisfactory level. Achievement of several or all of the objectives mentioned would provide a user interface control device which is superior to prior art devices.